I have recently moved in to a bungalow which was built approx 20 years ago.The problem is its taking approx 5 hours for the house to warm up but then its only reaching about 20 degrees max.The oil central heating bolier is less than 12 months old. All the radiators are getting hot - I was advised by a heating engineer that the radiators are not big enough to heat the rooms & need replacing this has been done but it has not made any differance also i was advised by another engineer to have the pump replaced as it was old. I have had this done & the hot water is getting hot quicker now & the radiators are slightly hotter but the house is not warming up.

"I was advised by a heating engineer that the radiators are not big enough to heat the rooms and need replacing this has been done"

Did he that gave you such advice fit the new rads? Did he specify the BTU requirements for each rad? If answer to these two questions is yes then perhaps you need to have a gentle but persuasive discussion with him.

Has this always been a problem ?
You say the bungalow is 20 years old - were the radiators the same age, if so then I'd imagine they would of worked well at some point so the radiator sizes were probably not to blame otherwise yourself/last owner would have done something about it before now.

All the radiators are getting hot ? how hot ?
Balance the system so there's an 11/12oC temperature difference between the flow and return.

Have you tried draughtproffing doors and windows, upgrading to double glazing if not already, insulating cavity walls and loft space ?

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